Information displays such as touch screen displays appear more and more frequently on interactive electronic devices. Reducing glare of the screens, a brightness caused by the reflection of incident light, is desired to maximize visibility of the displays in different lighting environments. There are various known methods of reducing the glare of transparent substrate surfaces. An exemplary method involves depositing a light interference coating stack on the substrate that reduces reflection by exploiting the optical interference within adjacent thin films. Such films usually have a thickness of about one-quarter or one-half the nominal wavelength of visible light, depending on the relative indices of refraction of the coatings and substrate. Interference coatings reduce glare without reducing resolution. However, they are relatively expensive to deposit, requiring the use of vacuum deposition techniques such as sputtering and precise manufacturing conditions, or very precise alkoxide solution dip coating techniques, with subsequent drying and firing steps. Strict processing parameters must be observed to obtain the desired results.
Another method of reducing glare on displays involves forming a light scattering means at the surface of the substrate, such as by mechanically or chemically altering the outermost surface of the substrate or through use of a diffuser coating or a glare reducing film on the glass substrate.
Some antiglare coatings cause an undesirable visual side-effect called visual sparkling effect, resulting from the interaction of light from a regular display pixel matrix with irregular microstructures present in the antiglare coating surface. Most antiglare surfaces such as acid-etched antiglare surfaces have a sparkling issue on high pixel per inch (PPI) displays.
Another option is the use of fillers. Fillers are widely used in the coatings industry to affect gloss and they are known to provide glare reduction to substrates in many cases. Fillers control gloss by affecting the surface roughness of an applied coating.
Etching the outer surface of the substrate or otherwise chemically or mechanically modifying the outer surface of a coating deposited on the substrate has also been attempted in an effort to reduce glare by diffusive reflection of light. There are numerous drawbacks to such modification techniques. Etching by chemical means involves handling and storage of generally highly corrosive compounds (e.g. hydrofluoric acid). Such compounds create processing and disposal problems in view of increasingly stringent environmental laws. Etching by non-chemical means, such as by sandblasting, necessitates additional and costly processing operations.
For touch screens such as those used on smart phones and tablets, a durable, anti-smudge coating is desired to ensure the cleanness and clarity of the touch screen surface. The anti-smudge coating is also expected to have a very smooth, silky, and slippery feel. Various super-hydrophobic coatings have demonstrated different degrees of anti-smudge properties and slipperiness. However, it is very difficult to achieve a better wear durability as tested using #0000 steel wool after more than 6000 cycles, and a coefficient of friction (COF) of ≤0.03.
It would be desirable to provide compositions that form an antiglare coating on a substrate while avoiding the drawbacks of the prior art, and to provide coated articles such as touch screen displays that demonstrate superior properties, including anti-glare.